1. Field of the Invention
The present invention relates generally to plant growing methods and containers, and more particularly, to methods and containers involving air-root-pruning of growing plants intended to be transplanted.
2. Description of the Prior Art
Landscape plants and other plants intended to be transplanted have for some time been grown out-of-doors in containers above ground. Container-grown plants can be grown at a faster rate than those grown in the field, and because the roots of container plants are not severed or otherwise disturbed when the plants are transplanted, such transplanting can take place at any time during the year, not just during the early spring as required with bare root or bagged nursery stock.
A variety of containers for growing plants intended to be transplanted have been developed and used heretofore, beginning with metal cans having holes punched in the bottoms and progressing to the present-day specifically designed plastic containers. However, problems experienced in growing plants in all such containers, especially woody plants, include spiral root growth and/or downward root orientation with little lateral root development. That is, as a lateral root grows in a container, its path is outward towards the side of the container and downward. When the root reaches a side of the container it follows the contour of the container to the bottom, and when it reaches the bottom, it often continues to grow in a circle. In some containers having open bottoms, the roots are air-pruned when they reach the bottom thereby substantially preventing spiral root growth, but the root tips are at the bottom of the container rather than along the sides. It has been shown that the root growth of container-grown plants after being transplanted primarily involves extensions of roots which were present in the container at the time of transplanting as opposed to the development of new roots. Consequently, the number and the position of root tips present at the time of transplanting is important to the rapid establishment, and frequently, the survival of container-grown plants.
Landscape plants have commonly been grown in square bottomless containers placed on wire surfaces whereby roots reaching the bottom of the container are air-pruned. However, most of the root tips produced end up at the bottom of the container, and the requirement of placing the containers on wire screen surfaces generally makes the practice uneconomical. Further, such open bottom containers are not easily moved without spilling or losing growth medium contained therein.
More recently, containers have been developed for controlling spiral root growth whereby the root tips are physically trapped by surfaces in the container and are prevented from elongating, or the circling root tips are caused to pass through vertical openings in the sides of the container whereby the tips are air-pruned. An example of the root trapping type of container is described in U.S. Pat. No. 4,442,628 issued Apr. 17, 1984. An example of a container including vertical side wall openings for air-pruning circling roots is described in U.S. Pat. No. 4,497,132 issued Feb. 5, 1985. While such root trapping and air-root-pruning containers have been utilized successfully, some spiral root growth still takes place and the development of lateral root tips has been less than optimum.
By the present invention an improved container for growing plants intended to be transplanted is provided whereby spiral root growth is prevented and the development of lateral root and branched root tips along and around the sides of the container is maximized.